1. Field of the Invention
The present invention relates to a four-wheeled motor vehicle and more particularly to a four wheel drive motor vehicle. More specifically, the present invention pertains to a driving torque distribution mechanism for a four wheel drive motor vehicle.
2. Description of the Prior Art
In a four wheel drive motor vehicle, it has been proposed to control the ratio of the torque distribution between the front and rear drive axles. For example, the Japanese utility model disclosure No. 56-122630 teaches to locate a slip clutch such as a wet type clutch or a fluid coupling in the torque transmitting path to the front and/or rear driving wheels. Where a wet type clutch is used, the torque to be transmitted through the clutch can be controlled by an adjustment of the engagement pressure between a pair of friction discs. In case where a fluid coupling is used, the torque to be transmitted through the coupling is controlled by an adjustment of the hydraulic pressure in the coupling.
In the Japanese patent disclosure No. 61-62641, there is disclosed another type of torque distribution mechanism. In the mechanism proposed by the Japanese patent disclosure, a plurality of differential gear mechanisms are provided in parallel in the torque transmitting path to the front and rear wheels and a selecting mechanism is provided to selectively bring one of the differential gear mechanisms into an operative position. The system as proposed by the Japanese patent disclosure is considered as preferable in respect to reliability and durability. It should however be noted that the structure as disclosed is not suitable for a vehicle having a transmission output axis arranged transversely with respect to the vehicle body.